matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs

{
  "id": "c05149f8be3e514607a278dfbd6ebc21933ed941bc13aa9af0b63fe4fbc0fcae",
  "url": "https://osv.dev/vulnerability/CVE-2023-38691",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs",
    "summary": "matrix-appservice-bridge provides an API for setting up bridges. Starting in version 4.0.0 and prior to versions 8.1.2 and 9.0.1, a malicious Matrix server can use a foreign user's MXID in an OpenID exchange, allowing a bad actor to impersonate users when using the provisioning API. The library does not check that the servername part of the `sub` parameter (containing the user's *claimed* MXID) is the the same as the servername we are talking to. A malicious actor could spin up a server on any given domain, respond with a `sub` parameter according to the user they want to act as and use the resulting token to perform provisioning requests. Versions 8.1.2 and 9.0.1 contain a patch. As a workaround, disable the provisioning API.",
    "evidence": "osv:CVE-2023-38691",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2023-38691",
      "aliases": [
        "CVE-2023-38691",
        "GHSA-vc7j-h8xg-fv5x"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/matrix-org/matrix-appservice-bridge",
              "type": "GIT",
              "events": [
                {
                  "introduced": "30f6e3a4f4c8e3ec0c4d08055e39845a71d34763"
                },
                {
                  "fixed": "48cf6d7ca4e8b0db2f738ce14014b4b34576906c"
                },
                {
                  "introduced": "533f27cb9a779a905b6b408ebd04f4c49963c84e"
                },
                {
                  "fixed": "4c6723a5e7beda65cdf1ae5dbb882e8beaac8552"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:matrix:matrix-appservice-bridge:*:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "4.0.0"
                      },
                      {
                        "fixed": "8.1.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:matrix:matrix-appservice-bridge:9.0.0:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "9.0.0"
                      },
                      {
                        "last_affected": "9.0.0"
                      }
                    ],
                    "source": "CPE_STRING"
                  },
                  {
                    "range": [
                      {
                        "fixed": "4c6723a5e7beda65cdf1ae5dbb882e8beaac8552"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "9.0.0",
            "= 9.0.0",
            "8.1.1",
            "8.1.0",
            "8.0.1",
            "8.0.0",
            "7.0.0",
            "5.1.0",
            "5.0.0",
            "4.0.1",
            "4.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-38691.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.480332484Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/38xxx/CVE-2023-38691.json",
        "https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x",
        "https://nvd.nist.gov/vuln/detail/CVE-2023-38691",
        "https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-287"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/38xxx/CVE-2023-38691.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2023-38691",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505581,
  "published_at": "2023-08-04T16:34:54.312+00:00"
}